CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (19,423)	$ (23,258)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	159	189
Non-cash lease cost	199	110
Share-based compensation	2,009	1,110
Unrealized foreign currency transaction (gain) loss	(19)	453
Accretion of discount on marketable securities	64	(53)
Changes in operating assets and liabilities:
Other receivables	(3,218)	5,036
Prepaid expenses and other current assets	869	(860)
Tax incentive receivables	772	(233)
Other assets		(1,224)
Accounts payable	2,689	4,824
Accrued expenses and other current liabilities	624	(9,287)
Other long-term liabilities	(9)	(44)
Operating lease liability	(195)	(92)
Net cash used in operating activities	(15,479)	(23,329)
Cash flows from investing activities:
Purchases of marketable securities	(2,997)	(3,995)
Proceeds from maturities of marketable securities	6,000	31,850
Purchases of property and equipment		(79)
Net cash provided by (used in) investing activities	3,003	27,776
Cash flows from financing activities:
Proceeds from equity offering	4,253
Payment of offering and financing costs	(37)	(352)
Proceeds from stock option exercises	93	539
Net cash provided by financing activities	4,309	30,186
Net increase (decrease) in cash and cash equivalents	(8,167)	34,633
Cash, cash equivalents and restricted cash at beginning of period	85,209	29,730
Cash, cash equivalents and restricted cash at end of period	77,042	64,363
Supplemental disclosure of non-cash activities:
Offering and financing costs in accounts payable and accruals	$ 93	109
Rights Offering [Member]
Cash flows from financing activities:
Proceeds from equity offering		9,416
Series C Preferred Stock [Member]
Cash flows from financing activities:
Payment of offering and financing costs		(41)
Supplemental disclosure of non-cash activities:
Series C issuance costs in accounts payable		41
Series C Preferred Stock [Member] | Rights Offering [Member]
Cash flows from financing activities:
Proceeds from issuance of Series C Preferred Stock related to Rights Offering		$ 20,583